Roof ridge ventilators, such as taught in U.S. Pat. No. 4,325,290, are recognized as valuable and useful roof installations for achieving desirable ventilation of the space below the roof of the building. The water vapor generated in the attic and which rises to the attic from within the building can escape through such an adequate ventilator system when in place. Of course, other roof ventilator systems of adequate construction may also function to enable escape of such water vapor in the attic or below the roof of the building.
However, such suitable ventilation systems are not used predominantly, especially in residential homes and in older buildings. The roof covering of such a building usually utilizes asphaltic-type shingles and coated underlayment sheeting and this type of roof covering is used both in new and remodeling applications. By their structural nature, such applications are intended to be waterproof so that water in liquid or vapor form will not penetrate through them. Thus, the desired characteristic of asphaltic-type roof coverings is to prevent passage therethrough of water and function as excellent vapor barriers.
This feature of conventional roof coverings contributes to a serious adverse condition in the building. For the past two decades, building construction has tended to focus on energy conservation. This focus has led to buildings that are substantially airtight, insulated and likely to permit exit of only a small amount of internally generated water vapor. For the most part, this trapped moisture driven by vapor pressure migrates to the attic where it is prevented from escaping to ambient atmosphere because of the lack of a suitable ventilation system, such as a ridge ventilator or other roof installed system. The trapped water vapor condenses to form free water on the underside of the roof and cause damage and deterioration of the structure in and below the attic.
According to the invention, there is provided a novel vapor permeable roof covering which substantially eliminates trapped moisture in an attic and significantly increases the longevity of the roof and building. The invention utilizes the considerable force of vapor pressure to enable accumulated attic vapor to exit the roof covering to ambient atmosphere and yet prevent free water from penetrating the roof covering into the attic.